Formatted Title
Field-Scale Application of a 200-m Horizontal Well to Recover DNAPL from Several Substratum Recesses
Background/Objectives
DNAPL often accumulate on clayey substratum it cannot penetrate. Clayey substratum rarely present a flat surface and most often DNAPL accumulate in topographic recesses. To reduce the mass of DNAPL source zone, all of the recesses must be emptied. Currently, this requires a good knowledge of substratum altitude and multiple vertical wells to empty every recess.
Approach/Activities
SERPOL associated to several partners in a national R&D project to assess the use of a horizontal well to recover the DNAPL trapped in several recesses using only one horizontal well crossing . The pilot study takes place on an industrial site where DNAPL (d1.6) accumulated in substratum recesses at a 10-m depth. Directional drilling is current in civil engineering but is only emerging for remediation activities. The well can be placed with a high precision often limited by the substratum altitude knowledge. Hence, for the pilot that will be presented, a precise map of the substratum altitude was constructed using geophysics methods (seismic and electrical) and validated using 40 geoprobe drilling. Several recesses, about 5 to 30 m wide and 50 cm to 1 m deep, were identified on the pilot zone. Based on the map, horizontal well placement was defined to cross three recesses. A 200 m long stainless-steel screened tubing was installed in the well by the GENDRY company. Pumping was then initiated at the lowest altitude point, collecting DNAPL from the three recesses and is now running.
Results/Lessons Learned
Setting up such a structure is different from typical vertical wells. It can offer the opportunity to quickly cross several recesses and offer higher pumping surface at substratum altitude than vertical drilling, though some unusual challenges for a remediation company must be considered (tubing material selection, drilling mud formulation and handling on site, sufficient clearance for tubing construction…). Hence, SERPOL will share its experience about the setup of such a novel structure and about the use regarding DNAPL recovery (including volumes pumped and evolution of the DNAPL interface altitude in crossed recesses). A preliminary cost-efficiency comparison to typical vertical wells will be discussed.